Process and apparatus for moving solid pellets
in a closed circuit



Sept. 13, 1966 F. NETTEL 3,272,335

PROCESS AND APPARATUS FOR MOVING sow) PELLETS IN A CLOSED cmcum FiledJuly 8, 1965 INVENTOR.

United States Patent 3,272,335 PROCESS AND APPARATUS FOR MOVING SOLIDPELLETS IN A CLOSED CIRCUIT Frederick Nettel, 173 Chapel Road,M'anhasset, Long Island, N.Y. Filed July 8, 1963, Ser. No. 293,544 3Claims. (Cl. 210-68) This invention deals with plants in whichcomminuted or granular solids are used for heating or cooling fluidsand/or gases which may be at pressures substantially above theatmospheric, with the solid circulating in substantially closed flowcircuits. The problem arises how to introduce the solids into the spacesunder pressure and/o1 how to withdraw them to spaces of lower pressure.

Transportation of such solids, which for the purposes of thisspecification shall be called pellets, across pressure differences isgenerally achieved either by powerdriven rotary feeders such as screwsor cell-wheels, or by the known sluicing system.

Rotary feeders have not been found suitable for large pressuredifferences for which only sequentially operated sluice chambers shallbe considered for the purposes of my invention.

In order to maintain pellet flow in a closed circuit, lifting of thepellet stream in part of the circuit is nearly always necessary. This isachieved either by conventional elevator devices, such as for examplebucket elevators, air jets working mostly near atmospheric pressures.These devices tend to damage the pellets by impact by the buckets orabrasion in the pipes guiding the pellets. Besides, the powerrequirements of these devices are very considerable.

This invention specifically refers to plans in which the pellets aresubmerged in a lower chamber containing a fluid under pressure fromwhich they must be lifted and led into another chamber at higherelevation, working at near-atmospheric pressure.

Lifting is effected by withdrawing from the lower chamber a slurry ofpellets in the liquid in such a way that the pressure in said lowerchamber provides most of power for the lifting. While this method, dueto the fact that the slurry can move at comparatively low speed throughthe conduit, drastically reduces the possibility of mechanical damage tothe pellets, another problem arises from the necessity to separate thepellets from the fluid and from the necessary de-pressurizing of thepellets before they can be fed into the chamber at higher elevationworking at near-atmospheric pressure.

It is the principal object of this invention to provide ways and meansto avoid or reduce the disadvantages of the known methods and apparatus,and to simplify operation. This and other objects of my invention willbe apparent from the following specification, when taken together withthe accompanying drawing, which shows by way of non-limiting example anembodiment of my invention:

The single figure of the drawing shows schematically a plant consistingof an upper chamber 1 for the heating of pellets and a lower chamber 6for steam generation through heat transferred from said pellets, withassociated equipment for the transportation of the pellets.

The present invention will be described for a steam boiler plant where astream of pellets, acting as heat transfer agent, moves in asubstantially closed circuit through a plurality of chambers located atdifferent vertical elevations and approximately in vertical alignment,the lowest chamber being partly filled with water and partly with steamunder pressure and pellets being led from the lowest chamber to at leasttwo elevated closed sluice chambers into which a slurry formed ofpellets and water from the lowest chamber is fed sequentially.

3,272,335 Patented Sept. 13, 1966 The basic object of my invention isachieved by lifting the said slurry from said lowest chamber to thelevel of two elevated sluice chambers, with a mojor part of the liftingforce supplied by the fluid pressure in the lowest chamber, and by usingsaid sluice chambers for screening the pellets in the slurry from mostof the water before discharging them at near-atmospheric pressure intoanother chamber at an elevation higher than the lowest chamber.

The sundry means used include a first upflow (riser) pipe connecting thebottom of said lowest chamber with the sluice chambers arranged inparallel. Each sluice chamber is equipped with a screen for separatingthe pellets from the bulk of the liquid under pressure. First valvesinterposed in said first pipe near the entrance to the sluice chamberscontrol the slurry flow through said pipe.

A second pipe (downcomer) connects the sluice chambers with the lowestchamber for returning the separated liquid under pressure into thelowest chamber.

Third pipe means connect the sluice chambers with the higher chamber fordischarging into it depressurized pellets from which the bulk of theliquid has been separated by the screens. Second valve means, interposedin said second pipe, control the liquid flow therethrough. Furthermore,third valves interposed in said third pipe, control the pellet flowthrough the latter.

A fourth pipe connects the two sluice chambers. Interposed in the fourthpipe is a throttle device for limiting the liquid flow between thesluice chambers and for ensuring that both chambers are always filledwith liquid. The throttle device is preferably adjustable.

The pressure in the sluice chamber receiving pelletliquid slurry will inmost cases be equal to that prevailing in the lowest chamber minus thestatic head between said chamber and the sluice chambers and thefriction loss caused in the riser pipe.

A pump is interposed in the second (downcomer) pipe to maintain slurryand water flow, respectively, through the system.

Only in exceptional cases the pressure in the sluice chambers may behigher than that in the lowest chamber. In these cases a slurry pump isprovided in the first (riser) pipe.

The valves in the first, second and third pipes are according to thisinvention sequentially operated as will be described in more detail asthis specification proceeds.

Modifications in specific applications depend primarily on the requiredlifting height of the slurry and the available pressure in the lowestchamber. Where this height times the specific gravity of thepellet-water slurry exceeds the available fluid pressure (aboveatmospheric), the difference in lifting work must be supplied by aslurry pump interposed in said first pipe. In this case the staticheight of the fluid column in the second pipe will usually suffice toreturn the water from the sluice chambers via the second pipe into thelowest chamber, so that no pump is required in said second pipe. If thestatic pressure in the second pipe is insuflicient, a pump has to beprovided in said second pipe, as mentioned before.

Where, on the other hand, the fluid pressure is substantially greaterthan the required lifting height times the specific gravity of thepelle-t water slurry, the sluice chambers will operate undersuperatmospheric pressure. In such case the differential between thefluid pressure and the slurry pressure in the elevated sluice chambersis sufficient to do all the lifting work and one pump only in the secondpipe will ensure return of the separated water into the lowest chamber.

A slurry pump in the first (riser) pipe may nevertheless be used forstarting purposes while the fluid pressure in the lowest chamber may beinsuflicient; such pumps 3 need be kept in operation only until thefluid pressure in the lowest chamber has risen sufficiently.

Reverting now in detail to the single figure of the drawing, thereference numeral 1 denotes an upright heat exchange chamber (pelletheater) with internal transverse baflles 2 for delaying the fall of thepellets. Hot gases enter the chamber 1 through an inlet 3 adjacent tothe bottom of the chamber and leave in a cooled state through a stack 4adjacent the top of the chamber. The upper part of chamber 1 alsoincludes an elevated inlet conduit 5 for admission of cool pellets.Below the upper chamber 1 another chamber 6 (steam generator) islocated, the same being connected to Chamber 1 through a vertical forkedpellet conduit 7. interposed in 7 are two pellet sluice chambers 8 and9. Each of these sluice chambers has pellet valves at its inlet, marked10 and F11, as well as at the outlet, marked 12 and 16. By propersequential operation of these valves, known per se, pellets can flow bygravity from chamber 1 into chamber 6 against the pressure prevailing inthe latter.

In the steam generator chamber 6 constant water level marked 14 ismaintained by regulating by conventional means, not shown, the feedwaterflow through the pipe 15 into 6. Within 6, located above the waterlevel, bafiies 2' are arranged which serve to superheat the steam risingfrom the water surface before said steam leaves through the pipe 45 foruse elsewhere.

Further, two other chambers 16 and 17 are arranged above the chamber 1for handling the pellet-water slurry which collects at the bottom of thesteam generator chamber 6. These slurry sluice chambers are providedwith inlets near the top and outlets near the bottom controlled by theslurry valves 18, 19 and 20, 21, respectively. At the bottom of 6 aslurry outlet pipe 22 is connected with the valves 18 and '19. Throughthis pipe, with interposed pump 23, the slurry can be lifted into thechambers 16 and 17. As mentioned before, the lifting work for the slurryis effected either partly or fully by the pressure prevailing in '6.

Inside the chambers 16 and 17 screens 24 and 25 are provided into whichslurry is discharged via the valves 18 and 19. Outlet pipes 26 and 27 atthe bottoms of said screens, in which the valves and 21 are interposed,lead concentrated slurry into the open hopper 28. Another screen 29 insaid hopper allows the water filling the interstices between theindividual pellets to drip off. The still surface-wetted pellets flowvia the conduit 30 into the dryer 31 where a fast air flow, produced bythe blower 32, removes residual moisture from the pellets which proceedby gravity via the conduit 5 into the upper chamber 1 through which theycascade downwards over the bafiles 2 being heated by the hot gases incounterflow heat exchange with the latter which leave cold through thestack 4.

Each of the chambers 16 and 17 is connected near its bottom via the'water pipe 33 with interposed three-way valve 34 to the downcomer waterpipe 65, which leads water back into the steam generator chamber '6 asshown. A water pump 36 may be interposed in pipe '35.

Drip water, accumulating at the bottom of hopper 28, is pumped back intothe pipe 35 via the pipe 37 with pump 38.

The hot gasses entering the pellet heater 1 through the inlet 3 may comefrom any source, including, for example, hot gases from chemical,metallurgical or other processes. In the plant as per the single figureof the drawing the gases are produced by combustion of fuel of any kind,supplied through the pipe 39, in air supplied by the forced draft airblower 40.

The sluice chambers 16 and 17 are further connected preferably neartheir tops via the water pipe 41, with adjustable valve 42, the purposeof which will be explained later.

The plant operates as follows: The sluice chambers 8 and 9 aresequentially filled with pellets from the bottom of the chamber 1 andthen discharged into 6. In the position shown (valve 1 1 open and valve1 3 closed) pellets can fall by gravity into chamber 9 and fill it. Inthe meantime the chamber 8, with valve 10 closed and valve 12 open andassumed filled with hot pellets, has been pressurized by steam from 6 sothat the pellets can flow by gravity into 6.

While the chamber 8 is being emptied, chamber 9 is being filled and whenthis is completed, valves 11 and 12 are closed, followed by opening ofvalves 10 and 13. Obviously, the role of the chambers 8 and 9 is nowreversed, chamber 8 being Lfilled from 1 and chamber 9 discharging into6. In order to save some of the steam under pressure remaining in theemptied chamber, a cross connecting pipe 43 between said chambers withinterposed valve 44 is provided. The valve 44 is only momentarilyopened.

The specific feature of this invention concerns the design and operationof the slurry sluicing and pellet separating chambers 16 and 17. Thesepreferably cylindrical chambers and the valves controlling theiroperation are basically of similar design as the chambers '8 and 9. Themain diiferenceslie in the provision of the screens 24 and 25, thevalved water discharge pipe 33, and the water cross-connection pipe 41with adjustable throttle orifice 42.

These chambers operate as follows:

Assuming slurry under pressure is supplied through the riser pipe 22,with .valves 19 and 20 open, valves 18 and 21 closed and the valve 3 4in the position as shown.

connecting the chamber 17 to the downcomer pipe 35, slurry will enterthe chamber.

The water which carried the pellets, passes through the screen 25 andthe valve 34 into the downcomer pipe 3 5 in a steady stream while thepellets accumulate in the space within the screen 25, filling this spacegradually.

Assuming also that such filling with pellets has previously taken placein the chamber '16, pellet concentrate from 1 6 can simultaneously flowvia the pipe 26 and valve 20 into the hopper 28. For smooth discharge itis necessary to prevent formation of a vacuum in 1-6. 'For this purposewater is introduced from 17 via the crossconnection 41 as long aspellets are discharged from 16.

After 16 is empty of pellets and '17 is filled 'with pellet concentrate,the valves 19 and 20 are closed, the valves 18 and 21 are opened, andthe chamber '16 connected to the downcomer pipe 3 5 via the valve 34while interrupting the water discharge from the chamber 17 via 34. Withthe closing of valve 20 the chamber 16- is pressurized through pipe 41,and with the opening of valve 18 pellets will start accumulating in itwithin the screen 24, repeat :iln7g the process as previously describedfor the chamber Simultaneously with the closing of the valve 19 andopening of the valve 21 pressure in 17 drops to nearatmospheric butwater flowing from the now pressurized chamber 16 enters 17 via the pipe41 keeping it filled with water.

This sequential operation of 16 and 17 can be continued indefinitelyassuring a practically continuous flow of pellet concentrate into thehopper 28. In the latter supplied by the fan 32 blows off most of thesurface moisture. The thus dried pellets are led into the pellet heatervia the conduit 5. The water separated in 31 may also be recovered byleading it back into the chamber 6.

The drying of the pellets is optional.

Characteristic for the present invention is the triple I use of thechambers 16 and 17.

(a) for depressurizing the slurry by sluicing,

(b) simultaneous formation of a slurry concentrate in I which waterfills only the interstices between the packed pellets,

(c) for returning the bulk of the separated water under pressure intothe steam generating chamber 6. It is immaterial for the presentinvention whether more than two sequentially operated chambers are usedin the slurry circuit, and what material and shape is employed for thepellets or whether a fluid dilferent from water is being evaporated. Itis further immaterial from what source the hot gases entering the pelletheater originate, or what fuel is used to produce said hot gases. Alsoimmaterial are the control means by which sequential operation isachieved.

Having now described and illustrated my invention, I wish it to beunderstood that it is not limited to the special form and arrangement ofparts herein described and shown.

What I claim is:

1. In the method of moving pellets, used as heat transfer agent,continuously in a closed circuit, said circuit comprising an upward flow(riser) part in which the pellets are lifted to a highest level, and adownward flow (downcomer) part, in which the pellets descend under theeffect of gravity, the upward flow part containing pellets suspended inthe form of a slurry in a rising stream of a liquid at substantiallysuperatmospheric pressure, while the first portion of the downward flowpart contains pellets falling through a gas of substantially atmosphericpressure,

the steps of passing the slurry stream through two sequentially operatedsluice chambers arranged in parallel and disposed at said highest level,said sluice chamber-s being at all times completely filled with liquid,separating the pellets from the bulk of the liquid by screening theslurry within said chambers and while still under substantiallysuperatmospheric pressure, thereafter decompressing the resulting slurryconcentrate Within said chambers, removing the remaining liquid from thepellets at substantially atmospheric pressure, and feeding the driedpellets at substantially atmospheric pressure back into the downwardflow part.

2. Apparatus for moving a continuous stream of solid pellets in asubstantially closed circuit extending between a lowestlevel and ahighest level, wherein the pellets move downwards under the effect ofgravity first through an upper space (first space) at near-atmosphericpressure and thereafter through a lower space (second space) containinga liquid at superatmospheric pressure, whereupon the pellets arereturned upwards in the form of a pressurized slurry formed by a mixtureof said pellets and said liquid, said apparatus comprising two sluicechamber means arranged in parallel with regard to said pellet stream anddisposed at its highest level, each chamber containing first screenmeans for separating the pellets from the bulk of the liquid underpressure, said screen means dividing each sluice chamber into a pelletchamber and a liquid chamber, first pipe means (riser) connecting thebottom of said second space with said pellet chambers for lifting theslurry from said second space into said sluice chambers, second pipemeans (downcomer) connecting said liquid chambers with said second spacefor returning the separated liquid under pressure, third pipe meansconnecting said pellet chambers with said first space for discharginginto it depressurized pellets from which the bulk of the liquid has beenseparated by said screens, fourth pipe means interconnecting the liquidchambers of said two sluice chambers, first valve means for controllingthe slurry flow from said first conduit means into said pellet chambers,second valve means for controlling the liquid flow from said liquidchambers into said second pipe means, third valve means for controllingthe pellet discharge from the sluice chambers into said third pipemeans, throttle means interposed in said fourth pipe means for limitingthe liquid flow from one sluice chamber into the other, hopper meanswith second screen means interposed in said third pipe means forseparating the remaining liquid from the pellets.

3. Apparatus as set forth in claim 2, having pump means interposed insaid second conduit means.

References Cited by the Examiner UNITED STATES PATENTS 2,682,497 6/1954Dutcher 165-107 X 3,219,105 11/1965 Nettel l*-106 REUBEN FRIEDMAN,Primary Examiner. SAMIH N. ZAHARNA, Examiner.

1. IN THE METHOD OF MOVING PELLETS, USED AS HEAT TRANSFER AGENT,CONTINUOUSLY IN A CLOSED CIRCUIT, SAID CIRCUIT COMPRISING AN UPWARD FLOW(RISER) PART IN WHICH THE PELLETS ARE LIFTED TO A HIGHEST LEVEL, AND ADOWNWARD FLOW (DOWNCOMER) PART, IN WHICH THE PELLETS DESCEND UNDER THEEFFECT OF GRAVITY, THE UPWARD FLOW PART CONTAINING PELLETS SUSPENDED INTHE FORM OF A SLURRY IN A RISING STREAM OF A LIQUID AT SUBSTANTIALLYSUPERATMOSPHERIC PRESSURE, WHILE THE FIRST PORTION OF THE DOWNWARD FLOWPART CONTAINS PELLETS FALLING THROUGH A GAS OF SUBSTANTIALLY ATMOSPHERICPRESSURE, THE STEPS OF PASSING THE SLURRY STREAM THROUGH TWOSEQUENTIALLY OPERATED SLUICE CHAMBERS ARRANGED IN PARALLEL AND DISPOSEDAT SAID HIGHEST LEVEL, SAID SLUICE CHAMBERS BEING AT ALL TIMESCOMPLETELY FILLED WITH LIQUID, SEPARATING THE PELLETS FROM THE BULK OFTHE LIQUID BY SCREENING THE SLURRY WITHIN SAID CHAMBERS AND WHILE STILLUNDER SUBSTANTIALLY SUPERATMOSPHERIC PRESSURE, THEREAFTER DECOMPRESSINGTHE RESULTING SLURRY CONCENTRATE WITHIN SAID CHAMBERS, REMOVING THEREMAINING LIQUID FROM THE PELLETS AT SUBSTANTIALLY ATMOSPHERIC PRESSURE,AND FEEDING THE DRIED PELLETS AT SUBSTANTIALLY ATMOSPHERIC PRESSURE BACKINTO THE DOWNWARD FLOW PART.